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ศาสตราจารย์์ ดร.มงคล เดชนครินทร์ 227

Abstract: Serial Data Exchange Between Microcontrollers Using only Two
Signal Wires
Professor Dr. Mongkol Dejnakarintra
Fellow of the Academy of Science,
The Royal Society of Thailand
This article presents a method for serial data exchange between
the 8088 Microcontroller Board (master board) and the PIC16F627A

Microcontroller Board (slave board). The 8-bit data byte is sent one bit at
a time consecutively from the sending board. The eight bits are combined
at the receiving board to retrieve the original data byte. About hardware,
the two microcontroller boards use only two cross wires for sending/receiving
control signals and data, but do not use additional two cross wires to check/
show readiness for data exchange as has been done in the author’s previous
article. The software in this present article uses a sync pulse for the master

board and the slave board to interrupt each other. This sync pulse precedes
a control/data bit code and coordinates the sending and receiving of the
code without using additional signal wires. When compared with the serial
data exchange scheme that uses four signal wires in the author’s previous
article, the procedure in this article has an advantage, namely, reduction of
signal wires from four to only two wires, but has a disadvantage, namely,
reduction of data exchange speed to lower than 1/4 of that used in the
four signal wire scheme. From a test in which the two microcontroller
boards were placed not farther than one foot apart, it was found that the

data reaching the destination board were correctly received, being the same
as those having been sent from the source board.

Keywords: microcontroller, serial data, interrupt, integrated circuit, 8088,
8255, 8259, PIC16F627A